The increasing hybridization of vehicles makes it necessary to make available electrical energy in the vehicle to a greater degree than is necessary in a conventional motor vehicle for operating electrical systems. Since insufficient electrical energy can be made available with contemporary battery technology, it is necessary to provide the vehicle with devices for acquiring and recovering electrical energy. For this purpose, inter alia, methods for recovering energy such as, for example, the recuperation of braking energy or the thermoelectric conversion of energy from waste heat which is produced in the combustion process are known. The thermoelectric conversion of energy takes place, inter alia, by utilizing the photoelectric effect, wherein the thermal radiation which is emitted by a hot component is converted directly into an electric voltage by means of photovoltaic cells. The photovoltaic cells which are typically formed from semiconductor materials are arranged here as close as possible to the heat source in order to obtain the highest possible energy yield. In this environment, these sensitive components are subjected to conditions which can have an adverse effect on the functional capability and/or efficiency of the photovoltaic elements. It is therefore possible, for example, for heat and various chemical substances to contribute to an accelerated ageing process of the photovoltaic elements which are typically formed from semiconductor materials. Furthermore, soiling of the photovoltaic elements can lead to a loss of efficiency due to shadowing effects. In addition, the further components of the thermoelectric system such as, for example, the cabling or the plug-type connections of the photo cells may also lead to a reduction in the efficiency level of the system due to ageing or owing to damage.
In order to detect such disruption of the thermoelectric system in good time and avoid losses during the recovery of energy by means of suitable countermeasures, it is appropriate to monitor the operating state of the thermoelectric system.